TypeInformation.java

/*
 * Copyright 2008-2015 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.springframework.data.util;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.util.List;
import java.util.Optional;

/**
 * Interface to access property types and resolving generics on the way. Starting with a {@link ClassTypeInformation}
 * you can traverse properties using {@link #getProperty(String)} to access type information.
 * 
 * @author Oliver Gierke
 */
public interface TypeInformation<S> {

	/**
	 * Returns the {@link TypeInformation}s for the parameters of the given {@link Constructor}.
	 * 
	 * @param constructor must not be {@literal null}.
	 * @return
	 */
	List<TypeInformation<?>> getParameterTypes(Constructor<?> constructor);

	/**
	 * Returns the property information for the property with the given name. Supports property traversal through dot
	 * notation.
	 * 
	 * @param property
	 * @return
	 */
	Optional<TypeInformation<?>> getProperty(String property);

	default TypeInformation<?> getRequiredProperty(String property) {
		return getProperty(property).orElseThrow(() -> new IllegalArgumentException(
				String.format("Could not find required property %s on %s!", property, getType())));
	}

	/**
	 * Returns whether the type can be considered a collection, which means it's a container of elements, e.g. a
	 * {@link java.util.Collection} and {@link java.lang.reflect.Array} or anything implementing {@link Iterable}. If this
	 * returns {@literal true} you can expect {@link #getComponentType()} to return a non-{@literal null} value.
	 * 
	 * @return
	 */
	boolean isCollectionLike();

	/**
	 * Returns the component type for {@link java.util.Collection}s or the key type for {@link java.util.Map}s.
	 * 
	 * @return
	 */
	Optional<TypeInformation<?>> getComponentType();

	/**
	 * Returns the component type for {@link java.util.Collection}s, the key type for {@link java.util.Map}s or the single
	 * generic type if available throwing an exception if it can't be resolved.
	 * 
	 * @return
	 * @throws IllegalStateException if the component type cannot be resolved, e.g. if a raw type is used or the type is
	 *           not generic in the first place.
	 */
	default TypeInformation<?> getRequiredComponentType() {
		return getComponentType().orElseThrow(
				() -> new IllegalStateException(String.format("Can't resolve required component type for %s!", getType())));
	}

	/**
	 * Returns whether the property is a {@link java.util.Map}. If this returns {@literal true} you can expect
	 * {@link #getComponentType()} as well as {@link #getMapValueType()} to return something not {@literal null}.
	 * 
	 * @return
	 */
	boolean isMap();

	/**
	 * Will return the type of the value in case the underlying type is a {@link java.util.Map}.
	 * 
	 * @return
	 */
	Optional<TypeInformation<?>> getMapValueType();

	default TypeInformation<?> getRequiredMapValueType() {
		return getMapValueType().orElseThrow(
				() -> new IllegalStateException(String.format("Can't resolve required map value type for %s!", getType())));
	}

	/**
	 * Returns the type of the property. Will resolve generics and the generic context of
	 * 
	 * @return
	 */
	Class<S> getType();

	/**
	 * Returns a {@link ClassTypeInformation} to represent the {@link TypeInformation} of the raw type of the current
	 * instance.
	 * 
	 * @return
	 */
	ClassTypeInformation<?> getRawTypeInformation();

	/**
	 * Transparently returns the {@link java.util.Map} value type if the type is a {@link java.util.Map}, returns the
	 * component type if the type {@link #isCollectionLike()} or the simple type if none of this applies.
	 * 
	 * @return
	 */
	TypeInformation<?> getActualType();

	/**
	 * Returns a {@link TypeInformation} for the return type of the given {@link Method}. Will potentially resolve
	 * generics information against the current types type parameter bindings.
	 * 
	 * @param method must not be {@literal null}.
	 * @return
	 */
	TypeInformation<?> getReturnType(Method method);

	/**
	 * Returns the {@link TypeInformation}s for the parameters of the given {@link Method}.
	 * 
	 * @param method must not be {@literal null}.
	 * @return
	 */
	List<TypeInformation<?>> getParameterTypes(Method method);

	/**
	 * Returns the {@link TypeInformation} for the given raw super type.
	 * 
	 * @param superType must not be {@literal null}.
	 * @return the {@link TypeInformation} for the given raw super type or {@literal null} in case the current
	 *         {@link TypeInformation} does not implement the given type.
	 */
	TypeInformation<?> getSuperTypeInformation(Class<?> superType);

	/**
	 * Returns if the current {@link TypeInformation} can be safely assigned to the given one. Mimics semantics of
	 * {@link Class#isAssignableFrom(Class)} but takes generics into account. Thus it will allow to detect that a
	 * {@code List<Long>} is assignable to {@code List<? extends Number>}.
	 * 
	 * @param target
	 * @return
	 */
	boolean isAssignableFrom(TypeInformation<?> target);

	/**
	 * Returns the {@link TypeInformation} for the type arguments of the current {@link TypeInformation}.
	 * 
	 * @return
	 */
	List<TypeInformation<?>> getTypeArguments();

	/**
	 * Specializes the given (raw) {@link ClassTypeInformation} using the context of the current potentially parameterized
	 * type, basically turning the given raw type into a parameterized one. Will return the given type as is if no
	 * generics are involved.
	 * 
	 * @param type must not be {@literal null}.
	 * @return will never be {@literal null}.
	 */
	TypeInformation<? extends S> specialize(ClassTypeInformation<?> type);
}